If you want to only use 1 filehandle you can always use a mixture of open/seek/tell/close to always re-use a single filehandle, see code below. Of course this is going to be really slow, as you will have to perform all 4 operations on every single line of each file.
Having a pool of open file handles would help some: as long as you are merging less files than the size of the pool you merge then the "natural way" (just read one line at a time from each filehandle), and if you need more, then you use the method below for files that you havent in the pool.
Does it make sense?
#!/usr/bin/perl -w
use strict;
use Fatal qw(open close); # so I don't have to bother testing them
my @files= @ARGV;
my %marker= map { $_ => 0 } @files;
while( keys %marker)
{ foreach my $file (@files)
{ if( exists $marker{$file})
{ open( my $fh, '<', $file);
seek( $fh, $marker{$file}, 0); # the 0 means 'set the new
+position in bytes to' $marker{$file}
if( defined( my $line=<$fh>))
{ print $line;
$marker{$file}= tell $fh;
}
else
{ delete $marker{$file}; }
close $fh;
}
}
}
|